Turbo ventilation



March .30, 192s.- 1,578,576

D. BRATT ET AL TURBO VENTILATI 0N Filed June 6, 1925 2 Sheets-Sheet 2 v -a.5 /9 5.5 Ely/4 L4 I I d WITNESSES" INVENTORS Dona/d flra/f and Cor/J fecbhe/mer ATTORNEY Patented Mar. 30, 1926.

UNITED STATES 'PATENT FFHQE.

DONALD BRATT, OF IRWIN, AND CARL J. FEOHHEIMER, 0F PITTSBURGH, PENNSYL- VANIA, ASSIGNORS 'I'O WESTINGRIOUSE ELECTRIC AND MANUFACTURING COM- PANY, A CORPORATION OF PENNSYLVANIA.

TURBO VENTILATION.

Application filed June 26, 1923. Serial No. 647,779.

To all whom it may concern:

Be it known that we, DONALD BRATT, a subject of the King of Sweden, and a resident of Irwin, in the county of \Vestmoreland and State of Pennsylvania, and CARL J. FECHI-IE'IMER, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsyl- Vania, have invented a new and useful I nprovement in Turbo Ventilation, of which the following is a specification.

Our invention relates to the ventilation of dynamo-electric machines, and it has particular relation to turbo-alternators and other smooth-core machines which are characterized by a relatively great length in comparison with the diameter, rendering ventilation by means of the air-gap alone insufficient.

In machines of the class just mentioned, it has been customary to supply the cooling fluid from both ends of the air-gap, discharging the same through radial ducts in the. stator. It has long been recognized that the ventilation from the ends of the air-gap could be supplemented by additional means for passing a cooling fluid into the intermediate parts of the air-gap through radial ventilating ducts in the stator, as set forth in the Swiss Patent No. 37,813, dated July 12,1906.

As a result of the difficulty of predicting the air flow and velocities in any given machine, as well as the very great cost of the machines, the machines of the prior art have been laid out without special consideration of the radial velocities in the most restricted portions of the respective radial ventilating spaces.

It 1s the principal object of our present invention to provide a machine of the class hereinabove described, wherein substantially uniform temperature conditions are secured by means of approximately uniform radial velocities of cooling fluid in the radial ventilating spaces of the stator.

Another object of our invention is to provide such a machine in which groups of radial spaces are arranged for intake ducts and discharge ducts, respectively, the number of ducts in each group having a definite relation to the ratio between the radial duct area and the air-gap area, all as hereinafter pointed out.

Other objects and details of our invention of the mathematical treatment of the prob-.

lem,

Fig. 3 is a curve diagram utilized in determining the relations of the various quantities involved,

Fig. 4: is another diagrammatic view ac-.

companying the mathematical treatment, and

Figs. 5 and 6 are curve diagrams illustrating our invention.

In Fig. 1 is shown a turbo-alternator comprising a stator member 10, carrying alternating-current windings 11, and a rotor member 12, carrying direct-current field windings, the end turns of which are shown at 13. The stator and rotor members are both of the smooth-core type, and they are separated by an air gap 14.

The stator member 10 comprises a laminated magnetizable core 15 having a large number of radially disposed annular ventilating spaces 16 left between bunches of laminations 17. The radial ventilating spaces or ducts are divided into a plurality of groups surrounded by annular chambers 18, 19 and 20, the central and end chambers discharge vents (not shown) andthe intermediate chamber 19 being an intake chamher for forcing a cooling fluid radially inwardly through the corresponding radial spaces 16.

Cooling fluid is supplied to the end bells I of the machine by any suitable means, such as fans 23 which are secured to the ends of the rot-01 member 12.

p the annular intake chambers 19 passes fa The intake chambers 19 arelikewise supplied with cooling fluid 20 and 18 being discharge chambers having dially inwardly to the air gap and thence divides and discharges through the radial ducts 16 associated with the adjacent annular disc'harge chambers 18 and 20, allas indicated by the arrows.

While prior constructions of the general type just described have had, for their object, the prevention of over-heating in the central portions of the machine, the designs have all been directed eitherto the problem of avoiding the necessity for utilizing the ventilating air after it had become'overheated in along passage throughthe air-gap to the central portions of the machine, or to the .problem of securinga sutiicient'airfiow without resort to excessive pressure-heads on account of the insuflicient air gap area in long .machines.

According to our invention, the cooling is eiiected very largely'by means of the radially flowing air, the axial flow being relied upon to a much lesser extent, and the quz-ur tity of air being such that its increase in temperature in the machine is relatively small. An important feature of our-invention is that we aim to obtain uniformity of temperature conditions within the machine by securing,-as nearly as possible, uniform radial velocities in the radial ventilating spaces. If any variation should occur in the radial velocities, it-is, of course, evident that somewhat lower velocities could'be tolerated in the intake vents than in the discharge vents, on account of the necessarily lower temperature ott-he intake air.

WVith the above-mentionedgeneral principles in view, our invention consists further in the discovery of certain relationships necessary'to 'existbetween the number of radial ventilating ducts in any group andthe ra'tio otthe ra'dial duct-area to the air-gap area,

our invention being the culmination of a long andcostly series of experiments. For

facilitating the explanation of our invention, reference will be made-to a mathemati' cal theory, with the understanding that we are not necessarily limited to any particulartheory-o'r explanation except as specified inthe appended claims.

Neglecting variations in volume resulting from pressure 1 and temperature changes, we may assume, with fair approximation, the validity of Bernoullis well-known equation im-hydraulics, namely, that the sum or" the .pressure headand the velocity head is a constant quantity for any particle throughout its course ina given duct. neglecting losses of head. Reference will be hadto the vt'ollowing notations, which will be made clearer by reference to Fig. 2:

w axial coordinate of intake belt.

g zaxi'al co ordinate of discharge belt. azstatic pressure in tube (air gap) 'at or y.

Pzstatic pressure in pressure chamber.

ozaxial air velocity in tube (air gap) at m or y.

'V radial air velocity in most restricted portion ofradia'lyent at m or-y.

azeross-sectienalarea oftube (air gap).

S:eross-section:ilarea 0'f:a radial vent at its most restricted section.

y spe'ciiic weight of air.

g:acceleration o1- gravity.

(l zintake coefiicient, definition:

Cd 'discharge coefiieient, definition:

r v d 9 L znumber of radial ventsin half' of intake belt.

L znumber'ot radial ventsin half of discharge belt.

The coefiicients' C, and C are introduced to compensate torthe friction losses andare constants depending upon the shape or" -"the slots, the number of teeth, the depth of punching,the shape of wedge, etc. 'l hecoefficients are constant'not'only tor 'anyJgiVen machine, but, in general, for any-size (it machine ota'given type, within the limits of pressure and velocity encountered in .practice. The terms (I, and C are evaluated largely by experiment. C appearstovary between the limits 1.05 and 1.30. for diit'erent machines andC appears to vary between the -limitsOiGOand 1.20. Itappears, from our present knowledge,thatC is'equal to a constant having a value of probably about 0.7 or 0.8;plus a constant times (S /a) The abovevalues are given for machines in which the slot wedgesare cut away wheretheycut the radial ventilating spaces 16.

From Bernoullis equation, we have 2 +2=const. v 9

Also, fronrthe definition 0t C we have, for

the intake,

which is substituted in equation (1), noting that (H is-a constant, giving const.

The equations (2) and (3) give there-la tion between 1) and V only. From the equation of continuity, we have ado: S.V.(Z00,

which means that the increase in volume in the air-gap equals the volume of air taken in through the radial ducts. The equations (2) and (3) are readily transformed into a differential equation of the second order in 'u and w, or (or in 'u and y, for the discharge). The solution of these differential equations and the proper determination ot the integration constants, give the following formulae each of which corresponds to any given group of radial ducts from the begin ning or end of the intake or discharge section to the balance point, or point at which the axial velocity becomes zero, as indicated in dotted lines in Figs. 5 and 6. The maximum axial air velocity is given, in each in stance, as 12 For the intake:

0 cosh (Swan-56 V- W g 5 5 w/ i Slllh cosh 'Lf (LVC -2 -'r. o

For the discharge;

sin l (ZJO v n ea cos 1y) l sin (Zn/C 2 d 00s am 2 vs the radial velocities approach a sinusoidal.

distribution, starting at avery low value in the radial vent nearest the end, and reaching a maximum at the balance point, as indicated in curve A in Fig. 5. The utilization of end gap ventilation is, therefore, not conducive, in general, to the production of optimum conditions with approximately uniform radial velocities.

An important feature of our invention is to rely principally, for the ventilation, upon the air fed from the stator, the air-gap being closed at both ends in the ideal case. By the employment or a relatively large number of annular intake and discharge chambers on the stator, as well as end ventilation on the air gap, the relative effect of the latter can be minimized to any degree desired. The occurrence of low radial velocities commonly resulting from end ventilation on the air gap can be avoided, in some measure, by proper design in accordance with principles explained later.

We will now explain the ideal arrangement of the stator ventilating system, assuming, for the moment, that the air-gap is closed at both ends. In such a system, a balanced arrangement would be employed wherein the balance points would all be in the centers of the intermediate sections and radial velocities in the intake and discharge ducts, respectively.

For the intake, V is a maximum for 02:0, and a minimum for xzL which, substituted in equation (5), gives min. h sin x C:

SL- max L i i c0 CIA/O i cosh M v mean Ii sinh J0 (L /U,

ma SL If we put SL, =a we we shall have for the intake,

max. min Cosh 0i 1 inean I h a For the discharge, V is a maximum for 7 :L and a minimum for 7 which, substituted :in equation (8) g1ves J1 Elie min.= 00b y '0 1 V ='\/Od' S111 (bx/Cd d COS d IL l Wm Vmean G I S dg 0 sm P9i. SL

If we put SL a,/(Td B7 we shall have, for the discharge,

max. min. 1 cos 6 w sinB I .2.1,/fi) and Assigning values to C, and C We find, for the particular machine in question, that the number of intake radial vents per halfsection, multiplied by the ratio of the minimum area of one radial vent to the area of the air-gap, should be about 0.9, and the corresponding number of discharge radial vents, multiplied by said ratio, should be 0.8. In general, from Fig. 3, it will be seen that any value of L2 less than unity will give fairly good results, where a very high degree of uniformity is not required. With an arrangement employing one center discharge, the radial vents would be grouped in the'order as indicated schematically in Fig. 4c.

\Ve will now consider a system of ventilation in which the air is fed both from the end-bell and from the stator. The formulae (4:) to (9) provide means for determining the axial and the radial air velocity at any point, and they thus provide means for so determining the length of the end discharge portion of the core in relation to the other discharges and intakes, that the ultimate variation in radial air velocity shall not exceed a certain proportion of the mean radial e have plotted the two functions,

and ,8,

SL O. 9== 7 (7/ /03 and SL 0.7 5 a /C Generally, S, a, C, and C are determined and fixed quantities. In -the case of the machines for Whichthe curves in Figs. 5 and 6 wereplotted, 3202 sq. ft., a:2.1 sq. ft, C 1-3O, Ca 1.07.

, or L =9.4:5 vents, say 9.5vents,

, or L =8.14 vents, say 8.5 vents.

air velocity. N 0 general proof can be given of this statement, as the work requires the solution of a system of simultaneous transcendental equations, which have to be solved by cut and trial.

As an illustration of the principles just explained, we have shown, in curve A of Fig. 5, the radial velocities of the ventilation as originally laid out, and we have superimposed, in curve B, an improved arrangement in accordance with our invention. It will be noted that the original arrangement gave very poor ventilation near the ends, with radial velocities running down to 400 feet per min. per one-inch of water pres sure. By the redesign in accordance with the principles'herein enunciated, utilizing a smaller number of ducts in the discharge groups at the ends, the initial radial velocity was brought up to 2300.

A further illustration ofa design in accordance with our invention is shown in Fig. 6, illustrating a very desirable arrangement in another stator frame.

The foregoing discussion is based upon the assumption that the rotor is stationary. Tests indicate that the-radial velocities are, if anything, more uniform when the'rotor is rotating.

lVhile'our invention has been described and explained with reference to a certain sistent with the im arovement over the prior art.

We claim as our invention:

1. A dynamo-electric machine having a rotor and a stator with an air-gap therebetween, said stator embodying a ventilating system comprising a plurality of groups of radially extending ventilating spaces surrounding the air-gap, intake chambers surrounding one or more groups of radial spaces for conducting a cooling fluid radially inwardly, and discharge means surrounding the remaining groups ot radial spaces, the cross-sectional areas of the airgap and radial spaces, the numbers of radial spaces in the respective groups, and the configurations of the ventilating paths being such that all groups have substantially the same minimum radial velocities and the same maximum radial velocities of the cooling fluid.

2. A dynamo-electric machine having a rotor and a stator with an air-gap therebetween, said stator embodying a ventilating system comprising a plurality of groups of radially extending ventilating spaces surroundingthe air-gap, intake chambers surrounding one or more groups of radial spaces for conducting a cooling fluid radially inwardly, discharge means surrounding the remaining groups of radial spaces, entrance chambers for cooling fluid at the two ends of the air gap, and means for maintaining approximately the same pressures in said intake and entrance chambers, the number of radial spaces in the end groups being so chosen with respect to the numbers of radial spaces in the intermediate groups and the ratio of the radial space areas to the air gap area, that approximately equal average radial velocities are obtained in all of the groups.

8. A dynamo-electric machine having a rotor and a stator with an air-gap therebctween, said stator embodying a ventilating system comprising a plurality of groups of radially extending ventilating spaces surrounding the air-gap, intake chambers surrounding one or more groups of radial s aces for conducting a cooling fluid radially inwardly, a discharge means surrounding the remaining groups of radial spaces, entrance chambers for cooling fluid at the two ends of the air gap, and means for maintaining approximately the same pressures in said intake and entrance chambers, the number of radial spaces in the end groups being so chosen with respect to the numbers of radial spaces in the intermediate groups and the ratio of the radial space areas to the air gap areas, that approximately equal minimum radial velocities are obtained in all of the groups.

4. The combination with a dynamo-elem trio machine having a rotor and a stator having an air-gap;therebetween, said stator having a plurality of radially extending ventilating passages surrounding said airgap, of means for supplying a cooling fluid to the peripheries ola plurality of radial passages and for discharging said cooling fluid-from a plurality of other radial passages, the intake radial passages being grouped in one or more sections and the discharge radial passages being grouped in a plurality of sections alternating with said intake groups, and the numbers of radial passages per group and the cross-sectional areas of the radial passages being so chosen that the diiierence between the maximum and minimum radial velocities in any group shall not exceed approximately thirty per cent of the average radial velocity in said group.

5. The combination with a dynamo-electric machine having a rotor and a stator having an air-gap therebetween, said stator having a plurality or" radially ext-ending ventilating passages surrounding said airgap, of means for supplying a cooling fluid to the peripheries of a plurality of radial passages and for discharging said cooling fluid from a plurality of other radial passages, the intake radial passages being grouped in one or more sections and the discharge radial passages being grouped in a plurality of sections alternating with said intake groups, the number of radial passages L per half-group of intake radial passages being approximately I i a L za-S. /0

a being an angle in radians such that cosh a- 1 slnh CZ of discharge radial passages being approxi mately =egqypa i ,8 being an angle in radians approximately such that and C being a constant determined by experiment for the particular mach ne, usually having a value between the limits 0.6 and 1.2 for different machines.

(ii The combination with a dynamo-electric machine having a rotor and a stator havin an air-gap therebetween, said stator having a plurality 0i radially extending ventilating passages surrounding said 31 1- gap, or" means for supplying a cooling fluid to the peripheries of a plurality of radial passages and for discharging said cooling fluid from a plurality oi other radial pas sages, the intake radial passages being grouped in one or more sections and the discharge radial passages being grouped in a plurality of sections alternating with said intake groups, and the number or radial passages per half-group, multiplied by the minimum cross-sectional area of a single radial passage and divided by the crosssectional area of the air gap, being less than unity.

7. The combination with a dynamo-electric machine having a rotor and a stator having an air-gap therebetween, said stator having a plurality of radially extending ventilating passages surrounding said airgap, of means for supplying a cooling fluid to the peripheries of a plurality of radial passages and for discharging said cooling fluid from a plurality of other radial passa'ges, the intake radial passages being grouped in one or more sections and the dis charge radial passages being grouped in a plurality of sections alternating With said intake groups, and the number of radial passages per half-group of intake radial passages, multiplied by the minimum cross-sectional area of a single radial passage and divided by the cross-sectional area of the air gap, being approximately 0.9.

8. The combination with adynamo-electric machine having a rotor and a stator having an air-gap therebetween, said stator having a plurality of radially extending ventilating passages surrounding said airgap, of means for supplying a cooling fluid to the peripheries oi a plurality of radial passages and for discharging said cooling fluid from a plurality of other radial passages, the intake radial passages being grouped in one or more sections and the discharge radial passages being grouped in a plurality of sections alternating with said intake groups, and the number of radial passages per halt-group of discharge radial passages, multiplied by the minimum cross-sectional area of a single radial passage and divided by the cross-sectional area of the'air gap, being approximately 0.8.

9. The combination with a dynamo-electric machine having a rotor and a stator having an air-gap therebetween, said stator having a plurality of radially extending ventilatingpassages surrounding said airgap, of means for supplying a cooling fluid to the peripheries of a plu'rality ot radial passages, and to the ends oi the air-gap and for discharging said cooling fluid from the remaining radial passages, the intake radial passages being grouped in one or more sections and the discharge radial passages being.

grouped in a plurality of sections alternating with said intake groups, the areas or the radial passages and the numbers of radial passages in the respective sections being so chosen with respect to the air-gap area that the ultimate variation in radial air velocity shall not exceed about thirty percent of the mean radial velocity.

In testimony whereof, we have hereunto subscribed our names this 14th day of June, 1923.

DONALD BRATT; CARL J. FECHHEIMER. 

